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ADDITION: Pedestal sink drain installation.

PS: In my question, I should have explained my concern that coupling the sink drain into the shower drain would not properly vent the sink drain. However, my own thinking is that, if you couple the sink drain pipe into the shower drain pipe above the p-trap, it will have the same effect as running the shower, and thus, the sink drain will be adequately vented.

Re: Pedestal sink drain installation.

I love these open forums. The questions are real. So I hope you simply take this as like something you might of overheard someone say at the hardware store isle (and not personaly). What you are also forgeting is the toilet. If you had an exsisting shower and toilet, this probably means the toilet is down stream of the shower and that the shower has the vent for both of the fixtures. Now adding the sink also means you will need to add at the very minimum a Studor Vent. If you do not do this the way the piping goes from the P-trap to the wall and then down means you will have an S-trap (and that is bad). Yes, the shower has the vent and can now carry all the fixtures (as long as it is 2"), but, if this were new construction or total remodel the lav or sink would of carried the vent for all three.

Re: Pedestal sink drain installation.

Thanks for your advice Misfitter. This is a small second bathroom enlarged to 6 x 6 feet, which would not likely have more than one person working one fixture at one time. The problem is not that the vent would be overwhelmed.

What I proposed was really a simple way of fooling the system by emptying the sink water (drain) into the shower drain above the shower trap. So who is the wiser. I'm not going to tell the toilet that it is the sink putting out that water instead of the shower. Still, we novices may not know everything we should.

Re: Pedestal sink drain installation.

Misfitter.

I have reevaluated my concern and now believe that it matters little whether a P trap (wall placed drain) or S trap (floor based drain) is involved. Since the sink will drain into the shower drain, there can be no sphoning of water in the traps if the drain enters the shower drain above its own trap. So I will not avoid an S trap in this situation. THe physics indicate that it makes no difference. Water in the trap of the sink cannot be sphiponed from the sink drain. Impossible physically.

Re: Pedestal sink drain installation.

Thanks for your feedback.

It seems to me entirely wasteful and expensive to introduce a new independent vent system for a sink that will be situated only 4-5 feet from a shower. The idea then is to couple the sink drain pipe to the shower drain pipe so that it can use the shower drain/vent system.

Would the problem you are alluding to be solved if the sink drain pipe were coupled into the shower drain AFTER the shower drain p-trap? This would leave the sink dependent on its own single trap. Thanks.

Re: Pedestal sink drain installation.

You want to install the drain after the shower trap other wise you could empty the sink into the base of the shower then install a studor valve as a vent for the lav. As Misfitter intimated it's not to code in some places but if you're doing it yourself......
Jack

Be sure you live your life, because you are a long time dead.-Scottish Proverb

Re: Pedestal sink drain installation.

Thanks Jack.

If I understand you correctly: the sink drain pipe should terminate in the shower drain AFTER the shower p-trap, and then employ a TUDOR vent to avoid siphonation in the sink trap. That sounds a lot cheaper than installing a roof vent for which I received and declined one estimate of $1600.